Implement subtype checks on type arguments.

sdk/lib/_internal/compiler/implementation/universe/universe.dart

Index: sdk/lib/_internal/compiler/implementation/universe/universe.dart
diff --git a/sdk/lib/_internal/compiler/implementation/universe/universe.dart b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
index 446d835cea79aa625319fcdbd7aa11d9f7ac9edc..13db4fbbbb7f80c824d1b27082c2821a93785e16 100644
--- a/sdk/lib/_internal/compiler/implementation/universe/universe.dart
+++ b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
@@ -34,7 +34,9 @@ class Universe {
    *
    * Invariant: Elements are declaration elements.
    */
+  // TODO(karlklose): these sets should be merged.
   final Set<ClassElement> instantiatedClasses;
+  final Set<DartType> instantiatedTypes;
 
   /**
    * Documentation wanted -- johnniwinther
@@ -52,6 +54,7 @@ class Universe {
   Universe() : generatedCode = new Map<Element, CodeBuffer>(),
                generatedBailoutCode = new Map<Element, CodeBuffer>(),
                instantiatedClasses = new Set<ClassElement>(),
+               instantiatedTypes = new Set<DartType>(),
                staticFunctionsNeedingGetter = new Set<FunctionElement>(),
                invokedNames = new Map<SourceString, Set<Selector>>(),
                invokedGetters = new Map<SourceString, Set<Selector>>(),